Copy-sheet and method

ABSTRACT

997, 362. Thermographic copying material and process. MINNESOTA MINING &amp; MANUFACTURING CO. Jan. 3,1962 [Jan. 3,1961], No. 10700/65. Divided out of 997,361. Heading G2C. A copy sheet or copysheet combination, which forms a visible image when heated but can be desensitized by exposure to ultra-violet radiation, contains (1) a normally solid organic salt of nickel, cobalt or copper and (2) N, N&lt;SP&gt;1&lt;/SP&gt;-bis-furfuryl-dithiooxamide or N, N&lt;SP&gt;1&lt;/SP&gt;-bis-carboxyamyl-dithiooxamide. Copies may be made by placing an original in contact with the copy sheet or combination, irradiating with infra-red while in contact, and subsequently desensitizing the copy by exposure to ultraviolet, or by exposing a copy sheet to ultra-violet through a transparent original bearing opaque markings, and subsequently heating to develop colour in the areas not so desensitized. The two reagents may be disposed in a single layer, in separate layers on a single carrier, or in separate layers on separate carriers. The reagent (1) may be nickel stearate or behenate. The reagents may be dispersed in a thin film of a resinous or polymeric film-forming binder in the form of a self-sustaining film, or as a coating on a backing of film, paper or the like. The Specification includes a list of suitable binders. The sheets may also include pigments, fillers, plasticizers, dyes, waxes and resins.

United States Patent 3,094,620 COPY-SHEET AND METHOD John Reitter, St.Paul, Minn., assignor to Minnesota Mining and Manufacturing Company, St.Paul, Minn., a corporation of Delaware No Drawing. Filed Jan. 3, 1961,Ser. No. 79,991 5 Claims. (Cl. 250-65) This invention relates toheat-sensitive copy-sheets and methods of making and using the same.

One well-known for copying typewritten ofiice correspondence and othergraphic originals having difierentially radiation-absorptive image andbackground areas is known as thermographic reproduction. It involves thebrief irradiation of the original, while sensitive copy-sheet, withhigh-intensity radiation. Preferential absorption of the radiation inthe absorptive image areas then results in localized heating of thecopy-sheet, producing a visible direct copy of the original. Thebackground areas of the copy-sheet remain heat-sensitive.

Another commercial 'oifice copying system requires preliminary exposureof a photosensitive sheet material to actinic radiation in a patterndetermined by an original having radiation-transmissive backgroundareas. Irradiated areas are thereby rendered non-reactive. The unexposedimage areas may in some instances be rendered visible by heating, butfor images of effective color density the sheet mustbe treated with afurther reagent or activator in liquid or vapor form. Apparatus forcarrying out the required sequence of operations is available under thedesignation Copy-Flex Model 100 copying machine. In this apparatus thecomposite of copy-sheet and transparency is passed over a rotating glasscylinder containing a mercury vapor lamp. Typically, a ,600 watt UA-20side of the axis of a glass cylinder having a 12 inch cir-' cumference,and the composite, in contact with the outer surface of the rotatingcylinder, is exposed over an arcuate path of 6 inches at a minimum speedofone inch in 5 seconds. Y

. Heat-sensitive copy-sheets have been described in which the visiblechange produced on localized brief heating is caused to occur by theinter-reaction ofa metal'saltand an organic chelating agent. Thereaction produces a strongly colored permanent image. As previouslydescribed, however, these copy-sheets have been found to remain visiblyheat-sensitive after, exposure to actinic radiation at speed in theCopy-Flex copying machine.

The present invention provides a heat-sensitive copysheet having avisibly heat-sensitive layer containing, in physically distinct andchemically inter-reactive relationship, a metal salt and an organicchelating agent capable of reacting together, in the thermographiccopying process or on momentarily heating the sheet to a conversiontemperature in the range of about 90 C. to about 150 C., with theformation of a visibly distinct reaction product, the reactants beingrendered incapable of undergoing such reaction on exposure to actinicradiation as provided in the Copy-Flex copying machine. The inventiontherefore makes possible the preparation of permanent, heatstable, highimage density reproductions of graphic originals by procedures involvingonly irradiation and without any necessity of treatment with solutions,fumes, vapors, powders or other adjuvants.

Typically, the composite of copy-sheet and original is first brieflyirradiated with intense radiation rich in infrared and in accordancewith known thermographic copying procedures. The thus imaged copy-sheetis next passed through the Copy-Flex copying machine under maximumexposure to the nearultraviolet radiation from the mer- 3,094,620 CePatented June 18, '1963 2 cury vapor arc. The resulting copy is stableagainst further heating to conversion temperature at the undarkenedbackground areas.

Copies may alternatively be prepared by first exposing the copy-sheet tothe near-ultraviolet through a transparency, for example a ribbon orcarbon copy of a typeand commercially important method inheat-conductive contact with a heatbacking,

separate backings.

Written document on thin semi-transparent paper, and then heating theentire copy-sheet to conversion temperature, for example on a heatedroller or platen or in an oven.

Dithiooxamide is known to be reactive with metal salts such as nickelstearate in the tom of heat-sensitive copy-sheets; but such products arefound to remain heatsensitive under exposureto near-ultraviolet as justdescribed. Surprisingly, it has now been found that substituteddithiooxarnide such as N,N'-bis furfuryl dithioox-amide are equallyelfectively, reactive with nickel stearate in copy-sheet formulations atconversion temperatures, while at the same time making possible thecomplete desensitization of the copy-sheet against such reaction by asingle pass through the Copy-Flex machine.

The substituted dithiooxamide and metal salt may be intimately dispersedin a thin film of a resinous or polymeric film-forming binder, either inself-sustaining film form or as a coating on a paper, film or otherpaper-like providing a unitary heat-sensitive copy-sheet in a singlecoating and drying operation. The two reactants may separately bedispersed or dissolved together with appropriate binders, and applied toa paper-like backing in separate coatings withintermediate drying, or toIn the latter case the two sheets when held in face-to-face contactpermit interfaci-al reaction at conversion temperature. The relativeamounts of the two reactants are not critical, particularly instructures wherein the image-forming reaction occurs at an interface,the only requirement being that sutlicient of each reactant be presentto ensure a readily visible change on reaction. It is desirable toemploya minimum amount of the substituted dithiooxamide and tomaintain'this material in position for maximum exposure to the actinicradiation. Various additives are useful in providing copy-sheets ofimproved appearance, handling characteristics, or other properties.Pigments, fillers, plasticizers, dyes, waxes, resins and other additivesmay be incorporated. H I Thefollowing specific examples will furtherillustrate but not limit the invention. Proportions are given in partsby weight.

EXAMPLEl Mixture A is prepared by prolonged milling in a ball mill, andis then coated in a thin uniform layer on map overlay tracing paper anddried. Mixture B is prepared by mixing the components together untilsolution is effected. The solution is then applied as a thin uniformcoating over the previous coating and the sheet is again dried. There isobtained a heat-sensitive copy-sheet having a neutral color. Localheating, as by momentary contact of the sheet with a metal test bar atC., causes intense darkening.

A portion of the copy-sheet is placed beneath a graphic originalprepared by typing on thin paper and the composite is irradiated inaccordance with thermographic copying procedure. A sharp and clearreproduction of the typed characters is obtained. The copy is thenexposed for approximately 30 seconds to intense near-ultravioletradiation bypassing it through the Copy-Flex copying machine at speed.The dark image areas remain unchanged. The background areas no longerdarken when placed in momentary contact with the heated test bar. I

A separate portion of the copy-sheet is placed beneath a printedtransparency prepared by typing on thin semitransparent paper, and thecomposite is exposed to nearultraviolet radiation by passing it throughthe Copy-Flex copying machine as before. With the copy-sheet andtransparency maintained in register, the composite is next brieflyirradiated as for thermographic copying. The resulting copy has sharplydefined dark image areas on a neutral background and is stable againstfurther heating at 150 C.

The image areas are equally readily developed by replacing thetransparency with a sheet of radiation-absorbent black paper prior toirradiating the composite with infra-red, or by placing the copy-sheetin contact with a heated metal platen or roller or in an oven heated toabout 150 C.

With N,N'-bis fu-rfuryl dithiooxamide and nickel stearate as thereactant materials, a purple image color is obtained. Nickel stearatewith N,N'-bis carboxyamyl dithiooxarnide provides a pink image. Othersalts of nickel, such for example as nickel behenate, produce similarresults. Salts of cobalt and copper are also useful. Other non-inventivevariations will be apparent in view of the foregoing disclosures.

The compound N,N-bis (furfuryl)dithiooxamide having the structuralformula HOCH HCCH Hii ii-oHPNH-o-o-NH-oHr-ii iii;

is similarly prepared using .dithiooxamide and aminocaproic acid.

What is claimed is as follows:

1. A heat-sensitive copysheet capable of undergoing permanent visiblechange on being momentarily heated to a conversion temperature withinthe range of about 90 C. to about 150 C. and of becoming insensitive tosaid heating on moderate exposure .to near-ultraviolet radiation, saidcopy-sheet including a visibly heat-sensilive layer containing, inphysically distinct and chemically inter-reactive relationship,chemically inter-reactant consisting essentially of nickel stearate andN,N-bis furfuryl dithiooxamide.

2. A unitary heat-sensitive copy-sheet capable of undergoing permanentvisible change on being momentarily heated to a conversion temperaturewithin the range of about 90 C. to about 150 C. and of becoming insenisitive to said heating on moderate exposure to near-ultravioletradiation, said copy-sheet comprising a thin paperlike backing and acoating comprising a film-forming binder and, in physically distinct andchemically interreactive relationship, chemically inter-reactantcomponents consisting essentially of nickel stearate and N,N'-'

bis furfuryl dithiooxamide.

3. Method of copying comprising placing in surface contact and inposition for irradiation a graphic original having ditierentiallyinf-rared absorptive image and back- 7 ground areas and a heat-sensitivecopyisheet having a visibly heat-sensitive layer containing nickelstearate and N,N-bis furfiuryl dithiooxamide in physically distinct andchemically inter-reactive relationship, momentarily irradiating saidgraphic original with intense radiation rich in infra-red for causingvisible inter-reaction in said i the near-ultraviolet wavelength regionand in localized background-defining areas sufiicient to render saidareas selectively insensitive to heat, and then heating at least theimage-defining areas of said layer to provide a visible image.

5. A radiation-desensitizable intermediate sheet product suitable foruse in the reproduction of a graphic original by a process involvingheating said sheet product, while in face-to-face contact with aseparate receptor sheet consisting essentially of a paper-like backingand a surface layer of nickel stearate, at areas corresponding toimage-forming areas of said original; the said intermediate sheetproduct consisting essentially of a paperlike backing and a surfacelayer of N,N'-bis furfuryl dithiooxamide.

References Cited in the file of this patent UNITED STATES PATENTS2,482,815 Urbach Sept. 27, 1949 2,813,042 Gordon et a1 Nov. 12, 19572,910,377 Owen Oct. 27, 1959 2,936,276 Chalkley May 10, 1960 2,950,987Howard Aug. 30, .1960 2,967,785 Allen et a1. Jan. 10, 1961

5. A RADIATION-DESENSITIZABLE INTERMEDIATE SHEET PRODUCT SUITABLE FORUSE IN THE REPRODUCTION OF A GRAPHIC ORIGINAL BY A PORCESS INVOLVINGHEATING SAID SHEET PRODUCT, WHILE A FACE-TO-FACE CONTACT WITH A SEPARATERECEPTOR SHEET CONSISTING ESSENTIALLY OF A PAPER-LIKE BACKING AND ASURFACE LAYER OF NICKEL STEARATE, AT AREAS CORRESPONDING TOIMAGE-FORMING AREAS OF SAID ORIGINAL; THE SAID INTERMEDIATE SHEETPRODUCT CONSISTING ESSENTIALLY OF A PAPERLIKE BACKING AND A SURFACELAYER OF N,N''-BIS-FURFURYL DITHIOOXAMIDE.